WIRING DIAGRAMS
NOTE
Polarity must be observed. If the HOT side of the second transformer is jumpered to the COMMON side of the first transformer a short will be made. Damage to equipment will occur when power is restored.
OBY2 Y1G
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Reversing | Valve | 2nd Stage | Fan |
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E/W1
W2
Emergency
Heat
C * | L | R |
SYSTEM
MONITOR 
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Limit or |
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| Safety | HOT |
Safety | 24 VAC |
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| 120 VAC | Switches |
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Switches |
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Valve | Energized in Compressor |
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Energized in | Heat, Off, |
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Cool Mode | Emergency |
| Compressor |
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Mode |
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Relay
Aux
Heat
Relay
SWITCH
24 VAC
ACCESSORY 
RELAY N.O.
CONTACT
COMMON
Auxiliary
Heating
Transformer
(Class II
Current Limited)
NOTE
The accessory relay scheme is required when safety circuits exist in both systems.
TWO COMMONS MUST
BE JUMPERED TOGETHER!
COMMON
Limit or
Safety
Switches
24 VAC
120 VAC
Limit or
Safety Switches HOT
NEUTRAL
Heat Pump Transformer
(Class II Current Limited)
Figure 4. Typical wiring diagram for two transformer heat pump systems with safety circuits in BOTH systems
*The 24 volt neutral connection to terminal C on the thermostat is not required if you replace the batteries once a year with fresh “AA” alkaline batteries.
Heat Pump Terminal Outputs
Refer to equipment manufacturers' instructions for specific system wiring information.
You can configure the thermostat for use with the following heat pump system types:
HEAT PUMP TYPE 1. Single stage compressor system; gas or electric backup.
This thermostat is designed to operate a
one transformer. If transformer safety circuits are in only one of the systems, remove the transformer of the system with NO safety circuits. If required, replace remaining transformer with a 75VA Class II transformer. After disconnecting one transformer, the two commons must be jumpered together.
Use the terminal output information below to help you wire the thermostat properly for your heat pump system. After wiring, see CONFIGURATION section for proper thermostat configu- ration.
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| THERMOSTAT TERMINALS (HEAT PUMP) |
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SYSTEM | L | C* | R | W2 | E/W1 | Y2 | Y1 | G | O | B |
Heat | Fault | 24 Volt | 24 Volt | Heat Mode | Emergency | No | Heat and | Blower/Fan Energized | Energized | Energized |
Pump 1 | Indicator | (Common) | (Hot) | 2nd stage, | Mode | Output | Cool mode | on call for Heat | in Cool | in Heat |
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| Emergency | 1st stage |
| 1st stage | and Cool | Mode | OFF |
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Heat | Malfunction |
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| 2nd | (compressor) | Set GAS/ELEC switch |
| Emergency |
Pump 2 | Switch |
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| Heat Mode |
| compressor |
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*The 24 volt neutral connection to terminal C on the thermostat is not required if you replace the batteries once a year with fresh “AA” alkaline batteries.
O | B | Y1 |
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Reversing |
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Valve |
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Energized in |
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Cool Mode |
| Heat Mode |
| Compressor |
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| Contactor |
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E/W1
Heat
Relay
Stage 1
W2
Heat
Relay
Stage 2
C * |
| THERMOSTAT | |||||||
R | SYSTEM | ||||||||
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| Hot |
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| 24 VAC |
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| 120 VAC |
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| Neutral | |
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Figure 5. Typical wiring diagram for single transformer
*The 24 volt neutral connection to terminal C on the thermostat is not required if you replace the batteries once a year with fresh “AA” alkaline batteries.
